First we find out in the pilot that Angela doesn't know how Rayanne used Jody Barsch, then in Halloween Angela is the only one who doesn't know about Nicky Driscoll. Is Angela just off in her own little world?

(Patty's query in the same episode may be of interest: "I mean, what is the eal with Rapunzel anyway? Is she a princess? Is she under a spell? What? I mean, all anyone ever remembers is that, that she has this really long hair and she was locked up in some kind of a..." Perhaps she has a selective memory when it comes to fairy tales or she only fixates on Cinderella. All I know is that I remember the story of Rapunzel including how she got stuck in the tower. Anyway, maybe cluelessness is genetic?)

Angela tends to often be caught in the moment. I don't think she's an airhead, just that she doesn't choose to pay attention to the things that everyone else is chattering about. Before she started hanging with Rayanne, Angela was likely a quiet girl who hung with Sharon and was constantly annoyed by Brian but didn't worry about much else. Teenagers are often caught in their own world and don't realize the biggest things going on around them.

i think that angela chooses to be clueless at times, in order to protect herself from information that she does not know how to deal with. the cloverdale house and what people do there both terrify her. if she admitted that she had heard about stuff like this, or thought about it, she'd have to explain why she was not taking part in it. also, being friends with sharon, but not being as gossipy as sharon, she was not exposed to a great deal of high school life until she met rayanne.

as far as being a princess, or being locked away in a tower, we know that both of her parents sort of wish that they COULD protect her in this way. the spaces that she is allowed to occupy throughout the show are very small and confined at first. she slowly starts to come out of her house and into the larger social and political and sexual world....
the show is a story of angela's growing up and getting to know herself and at the very end, getting to learn how to take on the responsibilities of her dreams. i think that "the substitute" and "guns and gossip" are both episodes in which we really see how angela is beginning to grapple with the adult world. to say that she is completely clueless is wrong. she is far more frank and honest with herself than a character like vic, and far more compassionate and insightful than ANYONE when it comes to talking to rickie about the gun.
also, the mere fact that angela writes the poem that she does implies that she knows that she is sheltered, and she's trying to figure out whether or not she wants to be.
sorry for rambling.....